The aircraft, which had just undergone its annual inspection, was observed in controlled flight before it began a slow descending turn which ended when it struck the ground. There were no mechanical deficiencies found that could have contributed to the accident. It can be concluded that the gradual descent was not the result of an airframe or control system failure. Based on the manner in which the aircraft descended to the ground and the post mortem examination which revealed well-established coronary artery disease, it is probable that the pilot suffered an acute coronary event during the flight. This resulted in incapacitation and the loss of control of the aircraft.Analysis The aircraft, which had just undergone its annual inspection, was observed in controlled flight before it began a slow descending turn which ended when it struck the ground. There were no mechanical deficiencies found that could have contributed to the accident. It can be concluded that the gradual descent was not the result of an airframe or control system failure. Based on the manner in which the aircraft descended to the ground and the post mortem examination which revealed well-established coronary artery disease, it is probable that the pilot suffered an acute coronary event during the flight. This resulted in incapacitation and the loss of control of the aircraft. The pilot most likely suffered an incapacitating medical event due to well established, underlying coronary artery disease that resulted in the loss of control of the aircraft.Finding as to Causes and Contributing Factors The pilot most likely suffered an incapacitating medical event due to well established, underlying coronary artery disease that resulted in the loss of control of the aircraft.